PROJECT SUMMARY AND ABSTRACT The vascular access is the lifeline for the hemodialysis patient. The most common etiology of vascular access dysfunction in hemodialysis patients is failure of an arteriovenous fistula (AVF) to mature successfully for dialysis use (AVF maturation failure). At present, there remains a very high rate of AVF maturation failure in the United States and there are no effective treatments to enhance AVF maturation. On a radiologic level, AVF maturation failure is most commonly characterized by a stenosis at the venous anastomosis, and at a histological level it is characterized by a combination of aggressive neointimal hyperplasia and poor outward remodeling. The poor outcomes following AVF creation reflect our limited understanding of the mechanisms leading to AVF maturation failure; and the lack of therapies to treat this clinical problem represent an unmet clinical need. The objective of this proposal is to understand the role of the endothelial nitric oxide synthase (NOS3)/nitric oxide (NO) system in AVF development. Preliminary work from our rodent AVF models has demonstrated: (1) impaired endothelial-dependent vasorelaxation (decreased NOS3-derived NO bioavailability) at the AVF anastomosis, (2) poor hemodynamic adaptation and biological responses in the setting of NOS3 dysfunction, (3) increased AVF neointimal hyperplasia and matrix metalloproteinase production in the setting of chronic kidney disease, and (4) reduced neointimal hyperplasia and improved vascular biological responses to a NO-releasing bionanomatrix gel applied directly at the AVF anastomosis during AVF creation. Based on these preliminary studies, the central hypothesis of this proposal is that the NOS3/NO system plays a critical role in successful AVF maturation by regulating local vascular hemodynamic adaptation and vascular biological responses after AVF creation; and locally delivered NO therapies applied at the AVF anastomosis can improve these two processes. Using our murine and rat AVF models, we will test our central hypothesis with two specific aims: (1) To determine how the NOS3 system modulates hemodynamic adaptation and biological responses during AVF maturation and (2) To evaluate the effect of a nitric oxide- releasing nanomatrix gel administered locally at the AVF anastomosis during AVF creation on enhancing AVF development. We believe our proposed research is significant because: (1) it addresses a very important clinical problem in hemodialysis patients, AVF maturation failure, where there are presently no effective therapies and (2) examines a fundamentally important system in AVF development, the NOS3/NO system. Successful completion of these aims will identify important targets for developing innovative therapies that aim to modify the NOS3/NO system in order to enhance AVF maturation. Our results will also have broad implications for other vascular conditions such as peripheral arterial disease, coronary artery disease, and postangioplasty restenosis.